Myelodysplastic Syndrome

Myelodysplastic Syndrome: Overview

Alternative names: Myelodysplastic Syndrome, MDS, Pre-leukemia, Preleukemia, Smoldering Leukemia

Preleukemia, or myelodysplastic syndrome (MDS), is a condition that can occur when some of the blood-forming cells in the bone marrow are damaged, leading to lower numbers of one or more type of blood cells.

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The bone marrow is spongy tissue inside some bones, such as the hip and thigh bones.  It contains immature cells, called stem cells, which can develop into the red blood cells that carry oxygen through the body, as well as the white blood cells that fight infection, and the platelets that help with blood clotting.  When a person has a myelodysplastic syndrome, the stem cells do not mature into healthy blood cells; many die in the bone marrow, leaving a deficit of healthy cells, which can lead to infection, anemia, or easy bleeding.

Because the majority (about two-thirds) of MDS patients do not develop leukemia, MDS was previously classified as a disease of low malignant potential.  Now that doctors have learned more about MDS, it is considered to be a form of cancer.

Incidence; Causes and Development; Contributing Risk Factors

The median age at diagnosis of a MDS is between 60 and 75 years; a few patients are younger than 50; MDS diagnoses are rare in children but a few pediatric cases have been reported.  Males are slightly more commonly affected than females.  Workers in some industries with heavy exposure to hydrocarbons such as the petroleum industry have a slightly higher risk of contracting the disease than the general population.

MDS occurs when the normally well-controlled production of blood cells is disrupted, resulting in blood cells that are immature and defective.  Instead of developing normally, they die in the bone marrow or just after entering the bloodstream.  Over time, the number of immature, defective cells begins to surpass that of healthy blood cells, leading to problems such as anemia, infections and excess bleeding.

Risk factors for MDS include:

  • Previous chemotherapy or radiation exposure
  • Being over 60 years old
  • Being male
  • Exposure to certain chemicals such as tobacco smoke, pesticides, and industrial chemicals such as benzene
  • Exposure to heavy metals such as lead and mercury
  • Children with Down syndrome are susceptible to MDS

Signs and Symptoms

Anemia dominates the early course of the disease.  Most patients who have symptoms complain of the gradual onset of fatigue and weakness, dyspnea, and pallor.  However, at least half the patients show no symptoms and their MDS is discovered only during routine blood tests.

Symptoms of MDS are nonspecific but include:

A blood count can show the following signs:

  • neutropenia (low white blood cell count)
  • anemia (low red blood cell count)
  • thrombocytopenia (low platelet count)
  • enlarged spleen (splenomegaly)
  • (more rarely) enlarged liver (hepatomegaly)
  • abnormal granules in cells
  • abnormal nuclear shape and size
  • chromosomal abnormalities, including chromosomal translocations and abnormal chromosome number

Diagnosis and Tests

The World Health Organization classifies myelodysplastic syndromes under subtypes based on the type of blood cells involved: red cells, white cells or platelets.  The subtypes include:

  • Refractory cytopenia with unilineage dysplasia
  • Refractory anemia with ringed sideroblasts
  • Refractory cytopenia with multilineage dysplasia
  • Refractory anemia with excess blasts – types 1 and 2
  • Myelodysplastic syndrome, unclassified
  • Myelodysplastic syndrome associated with isolated del(5q) chromosome abnormality

MDS must be differentiated from anemia, thrombocytopenia, and leukopenia.  Diagnostic investigation can include:

  • Full blood count
  • Examination of blood film
  • Blood tests that help eliminate other causes of cytopenias, for example lupus, hepatitis, B12, folate deficiency, other vitamin deficiencies, renal failure or heart failure, HIV, hemolytic anemia, monoclonal gammopathy
  • Cancer screening for anemic patients
  • Bone marrow examination
  • Cytogenetics or chromosomal studies
  • Interphase FISH testing, usually ordered together with conventional cytogenetic testing
  • Flow cytometry
  • Testing for copper deficiency, as it can resemble MDS in bone marrow biopsies.

Fever and weight loss should point to a myeloproliferative rather than myelodysplastic process.

Treatment and Prevention

There is no cure for myelodysplastic syndromes.  The goals of therapy are to control symptoms, improve quality of life, improve overall survival, and decrease progression to acute myelogenous leukemia (AML).

Prognosis; Complications

The outlook for MDS is poor; most patients will progress to acute myeloid leukemia within a few months.  The survival rate varies from years to months; stem cell transplantation offers cure, with survival rates of 50% at 3 years, although older patients do poorly.

Possible complications include:

  • Reduced numbers of red blood cells can cause anemia
  • Having too few white blood cells increases the risk of serious/recurring infections
  • Low platelet levels in the blood can lead to excessive bleeding that won't stop
  • Some people with myelodysplastic syndromes may eventually develop leukemia, a cancer of the blood cells

On This Page

Myelodysplastic Syndrome:

Myelodysplastic Syndrome can lead to:

Lab Values


The most common type of granulocyte (white blood cell with granules) in bone marrow is the neutrophil.  In cases of Myelodysplastic Syndrome, the blood-forming cells in the bone marrow become abnormal, often leading to Neutropenia (a low number of neutrophils in the blood.)

Tumors, Malignant

Acute Myelogenous Leukemia (AML)

About one-third of patients with Myelodysplastic Syndrome (MDS, or preleukemia) will develop overt leukemia – a rapidly growing cancer of bone marrow cells called acute myeloid leukemia (AML).

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